Method and apparatus for removal of tars or resins from a scrubber liquid

ABSTRACT

The invention is a method of processing tarry or resinous liquids. Tarry liquids include wet scrubber liquids containing tars and chars derived from gasification, pyrolysis or drying of biomass. Resinous liquids include those derived from processing coniferous biomass. Tarry or resinous liquid is processed by a horizontal axis centrifuge having a discharge chamber containing a scraper to prevent centrifuge clogging or fouling. The removed tar and char can be used as solid fuel or recycled to the gasification or pyrolysis process. Polymers, for instance cationic polymers, can be added to the tarry or resin containing liquid prior to centrifugation to assist in solids/liquids separation. Removed resin can be recycled for further use. Tar, char or resin depleted wet scrubber liquid can be recycled for further use or more easily treated prior to disposal.

REFERENCES CITED Foreign Patent Documents

CN101607780(A)-2009-12-23 Jihong Zhang Int. Cl. C02F1/24

JP2207098353(A) 2007-04-19 Ito Kimio Int. Cl. B01D17/00

U.S. Patent Documents

U.S. Pat. No. 2,366,899 1945-09-01 E. L. Hall 252/346

U.S. Pat. No. 7,915,458 1997-04-28 Peter Bruckmayer 568/840

U.S. Pat. No. 4,206,186 1980-06-03 Heinz Holter 423/230

U.S. Pat. No. 4,282,096 1981-08-04 Burkert 210/182

U.S. Pat. No. 4,364,796 1982-12-21 Yoshiaki Ishii 201/4

U.S. Pat. No. 5,897,689 1998-04-08 Emil Wieser 95/152

U.S. Pat. No. 7,626,069 2008-02-12 Thomas Nissen 585/802

US20040220285 2002-08-22 Harold Boerrrigter 518/726

US20070007170 2005-07-08 Robert S track 208/106

FIELD OF THE INVENTION

The present invention relates to a method and a device for separating carbon, hydrogen and oxygen containing tars and/or char from syngas wet scrubber liquids such as those derived from gasification or pyrolysis of biomass containing feedstocks including municipal solid waste or agricultural wastes including wood wastes. The invention also relates to a method and device for removing resins from biomass derived resin containing liquids such as those derived from a coniferous source, for example, including spruce or pine. The solid discharges from the device can be used as such or pelletized for a variety of applications and markets.

DESCRIPTION OF THE PRIOR ART

It is known that waste to energy plants, for example biomass waste to energy plants, very often use the wet scrubber technique for cleaning the syngas of tar and/or char so that the syngas is more suitable for use as a fuel. The gas leaving the gas-making apparatus, e.g. gasifier or pyrolyzer, is usually brought into contact with liquid or a process derived liquid such as in a wet scrubber, for example an aqueous liquid i.e. containing water. Since a water containing scrubber solution is hydrophilic and the tar and/or char or resin are hydrophobic and semi-hydrophobic i.e. semi-hydrophilic, the scrubber liquid converts to a tarry suspension in water.

The resinous or tarry suspension of resin or tar and/or tar containing hydrophilic liquid such as water is extremely difficult to handle by prior art techniques including concentration, filtration, absorption, thickening, use of cyclones or dehydration. The product remains extremely hazardous if spilled into the environment. The resinous or tarry suspension may contain as much as 99.5% liquid or even higher. Alternatively, the resinous or tarry suspension may be in the form of a pasty, sticky, high viscosity resinous or tar/char greasy solid of up to 35% solids.

Untreated spent tar/char/liquid tarry suspensions derived from syngas wet scrubbers cannot be disposed of to the environment due to the content of tar, including mono-aromatic and poly-aromatic hydrocarbons and phenols. These components are toxic in bio-treatment systems and are possibly poisonous or carcinogenic.

According to a study published by the National Renewable Energy Laboratory, currently available technologies for tar removal do not meet the needs of the industry in terms of cost, performance, and environmental considerations (T. A. Milne, et. al., “Biomass Gasification Tars, Their Nature, Formation, and Conversion”, NRELITP 570-25357, November 1998). Devi et al further illustrate problems associated with handling tars derived from biomass processing (“A Review of the Primary Measures for Tar Elimination in Biomass Gasification Systems”, Biomass and Bioenergy, 2003. 24(2):125-140).

Accordingly, a need exists for a method of and a device for treating this waste stream in an effective and simple way.

SUMMARY OF THE INVENTION

The current invention is a method and apparatus for cleaning resin or tar/char or tar-bearing scrubber liquids including scrubber liquids containing tarry or resinous suspensions containing water and tars containing hydrocarbons for example mono-aromatic or poly-aromatic hydrocarbons and phenols, naphthalenes or resins. The tarry suspension is processed in a continuous feed horizontal axis centrifuge, to create tar/char or resin depleted liquid for recycle as syngas scrubber liquid or for treatment prior to discharge. The continuous feed centrifuge also produces a liquid depleted centrifuge cake (tarry or resinous solids) for use as fuel, recycle to the gasifier or pyrolysis process to generate additional syngas or in the case of resinous solids for further use e.g. varnish or lacquer raw material. The continuous feed centrifuge contains a slow moving scraper in its discharge section to prevent clogging or fouling by the cake tar/solids unlike a centrifuge such as the scraper-free horizontal-axis type described in U.S. Pat. No. 7,915,458 to Bruckmeyer or the decanter centrifuge described in U.S. Pat. No. 5,897,689 to Wieser-Linhart.

The following non-limiting example illustrates one use of the current invention:

FIG. 1 illustrates a horizontal axis centrifuge 1 which can be used for separating feed tarry or resinous suspension 4 via inlet 11 into cleaned liquid 2 and tarry solids 13. The centrifuge 1 includes a horizontal rotation axis 3 and two bearings 5 and 6 on which a bowl 7 is rotating. Within bowl 7 there is a rotatable screw 8 that is supported rotationally with respect to the axis 3 by two bearings 15 and 16. The horizontal axis centrifuge 1 provides a centrifugal G-force of 1500 to 3200 on resinous or tarry suspension 4 introduced via inlet 11. Screw 8 turns inside bowl 7 with a different speed than the bowl. Bowl 7 is driven by a motor 18 via pulley 19. Screw 8 is driven by a pulley 20 and via gearbox 14 allowing for a different speed between bowl 7 and screw 8. A hydraulic or electric motor, with differential speed control, can be used as a substitute for pulley 20. Bowl 7 is provided with a liquid phase outlet 9 and a tarry or resinous solids phase outlet 10. Outlet 9 of cleaned liquid 2 may be provided with an adjustable weir disk or plate 12 at the rear wall of bowl 7, and the tarry or resinous solids outlet 10 is provided at the opposite wall of bowl 7 with a conical section 7 a. Screw 8 serves as a transportation means for material along the cylindrical, non-conical 7 b section of bowl 7, radially and inwardly along the conical bowl section 7 a towards the outlet 10. Tarry or resinous suspension 4, with or without polymer (e.g. cationic polymer) added to agglomerate solids, introduced through inlet 11 at the centre of the centrifuge axis, is introduced the centrifuge bowl 7 at feed point 17. The cleaned liquid 2 is discharged via the outlet 9 across the adjustable weir disk 12, or straight out when no weir disk or weir plate is used. The tarry or resinous solids 13 are discharged via screw 8 along conical bowl section 7 a through outlet 10 contained in discharge chamber 21.

FIG. 2 illustrates a scraper used in combination with the components of the apparatus illustrated in FIG. 1. Scraper 24 of scraper assembly 25 serves to prevent deposition of tarry or resinous solids inside discharge chamber assembly 21 and discharge chamber sub-assembly 23 via separate turning movement from bowl 7 or screw 8 via motor 22. FIGS. 1 and 2 illustrate the relative buildup of tarry or resinous solids inside the discharge chamber subassembly 23 with and without scraper 24 respectively. Lack of scraper 24 together with scraper assembly 25 results in uncontrollable, and undesirable repetitive fouling of discharge chamber assembly 21 and its subassembly 23.

The following 3 non-limiting examples describe the current invention:

Example 1 Processing of Tarry Wet Scrubber Liquid Suspension Derived from Municipal Solid Waste Biomass Gasification

Tarry suspension containing 0.5% solids by weight was input to the apparatus described in FIGS. 1 and 2 above with the following resulting output streams:

-   -   cleaned liquid having a solids content of milligrams/litre         suitable for recycling, treatment or discharge     -   powdery solids containing 75% solidshaving a heating value of         ˜25 megajoules/kilogram and suitable for use as fuel or for         recycling into the gasifier

Example 2 Processing of Tarry Wet Scrubber Liquid Suspension Derived from Wood-Chip Gasification

Tarry suspension containing 20% solids by weight was input to the apparatus described in FIGS. 1 and 2 above with the following resulting output streams:

-   -   cleaned liquid having a solids content of ≦10 milligrams/litre         suitable for recycling, treatment or discharge     -   tarry solids, containing 73% solids, having a heating value of         ˜25 megajoules/kilogram and suitable for use as fuel or for         recycling into the gasifier

Example 3 Processing of Resinous Liquid Suspension Derived from Drying of Coniferous Biomass Solids

In the drying process of coniferous biomass, e.g. spruce or pine, aromatics and resins go in the vapour phase, and are partially condensed by reducing the temperature. However much resin, especially resin molecules that condense at lower temperatures remain in the vapour stream. This vapour can be scrubbed with water to remove its contained resin and the resulting resinous water scrubber liquid can be fed into the horizontal axis centrifuge described in this invention to separate the contained resin in whole or part from the scrubber liquid. The scrubber liquid can then be recycled in whole or part or further treated in whole or part. 

I claim:
 1. A method of cleaning tarry or resinous liquid suspensions wherein the method of separating the tarry or resinous solids from the liquid contained in the suspension is via a centrifuge containing a separately moving bowl, feeder screw and a discharge chamber scraper that prevents fouling of the centrifuge discharge chamber by tarry or resinous solids.
 2. The method of claim 1 in which the centrifuge is a horizontal axis type.
 3. The method of claim 1 in which the liquid suspension is a wet scrubber liquid containing tar and/or tar/char solids.
 4. The method of claim 1 in which the liquid suspension is a resin containing liquid derived from coniferous biomass solids.
 5. The method of claim 1 in which the liquid suspension contains water.
 6. The method of claim 5 in which the liquid suspension is a spent water scrubber derived from gasification or pyrolysis of biomass.
 7. The method claim 2 in which the centrifuge has a g-force of 1500 or more.
 8. The method of claim 2 in which the centrifuge has a g-force of 3200 or less.
 9. A horizontal axis centrifuge containing a separately moving bowl, feeder screw and a discharge scraper that prevents fouling of the centrifuge discharge chamber by tarry or resinous solids. 